| Cu crystallites supported on activated carbon, graphitized carbon fibers, and synthetic diamond powder were investigated as possible replacement catalysts for copper chromite, which is commonly used as a catalyst for the selective hydrogenation of carbonyl bonds. In the hydrogenation of furfural to furfuryl alcohol, all Cu/C catalysts showed 100% selectivity towards hydrogenation of the carbonyl bond, and Cu dispersed on activated carbon showed superior activity maintenance characteristics.;Electrical characterization techniques including electron spin resonance (ESR) and electrical conductivity measurements via a microwave cavity perturbation technique were used to characterize the carbon supports and copper dispersed on silica. By measuring ESR spectra of activated carbons in which the surface was tailored to either significantly enhance the density of surface groups or cleaned of all surface groups, it was shown that ESR is an excellent tool to characterize the detailed microstructure of the surface for these high-surface area carbons. Another important finding was the semi-metallic electrical behavior of activated carbons, i.e., the activated carbons showed an increasing electrical resistivity with increasing temperature in contrast to typical semiconductor behavior.;Dielectric measurements on the pure silica (and pure alumina) powder indicated that the dielectric constant of these dielectric particles is significantly lower than the dielectric constant of the bulk material. The electrical conductivity of the copper crystallites linearly varied as a function of the crystallite volume. This indicates the occurrence and dominance of quantum confinements leading to discretization of the energy spectra (as a consequence of the localization of electrons due to a reduction in the crystallite size) over a purely classical scattering effect in this size range.;The effect of the metal loading and the particle size was studied in two reactions; acetone hydrogenation and N2O decomposition by utilizing the Cu/SiO2 catalysts characterized in the dielectric studies. Acetone hydrogenation displayed a dependence on the Cu crystallite size, with the catalyst having 110 nm Cu crystallites showing turnover frequencies 40 times greater than the one with Cu crystallite sizes between 1 and 2 nm. N 2O decomposition, on the other hand, was not structure sensitive on these Cu/SiO2 catalysts. |
